1. Field of the Invention
The present invention relates to a memory card having a plurality of electrically erasable type PROMs (EEPROMs).
2. Description of the Related Art
When a memory card is constructed by using a flash type EEPROM chip as a memory medium, the memory card can have a large capacity at a relatively low cost. However, the speed of a data writing operation of the EEPROM chip is low so that no high speed writing operation such as a writing operation of data of a compressed moving picture in real time can be realized at present.
For example, each of Japanese Patent Application Laying Open (KOKAI) Nos. 3-265287 and 4-268284 shows a technique for solving this problem. Japanese Patent Application Laying Open (KOKAI) No. 3-265287 shows a region for recording information indicative of the position of an empty unit recording region to be first recorded when image data are recorded to a semiconductor memory of a memory card. A writing speed of data is increased by retrieving the empty unit recording region for a short time. In Japanese Patent Application Laying Open (KOKAI) No. 4-288284, image information is written to a plurality of EEPROMs in parallel with each other so that each of the EEPROMs operated at a low speed can be used in real time as a high speed image recording medium.
However, write times of the EEPROMs are generally dispersed in accordance with EEPROM chips. Further, a write time of each of the EEPROMs is dispersed within the same EEPROM chip. Therefore, no efficient high speed writing operation can be performed even when a parallel writing technique is simply used. Accordingly, it is necessary to use a writing control system in which dispersion in performance of each of the EEPROM chips is considered.
In the case of the flash type EEPROM, the number of writing operations is limited so that a defective bit is caused when the flash type EEPROM is used for a long period. Therefore, it is necessary to arrange a certain defective control means so as to recognize a defective area on a systematic side within the memory card. However, in a general memory structure, defective information is simply stored to a certain area or region of a memory of the same kind, concretely, a file control area.
In general, the file control area in the memory is an area often accessed in comparison with a data area. Therefore, there is a high possibility that the file control area itself first becomes defective. Accordingly, when the file control area becomes defective within the memory card in such a memory structure, there is a problem that previously recorded data are invalidated after the file control area has become defective.